Polyvinylidene Fluoride is commonly used to produce tube products for wire and cable applications, as well as for jackets and primary insulation on wire and cable products. Copper, fiber optic, and plenum cables and conduit exist in large numbers in most commercial buildings. In the case of tubular structures, a common product referred to as a corrugated innerduct, is used for routing fiber optic cables in buildings. The current product is a solid PVDF tube that contains corrugations. Polyvinylidene fluoride (PVDF) is the preferred material for conduit used in these plenum applications because of its inherent toughness, inertness, and especially its flame and smoke resistance. Other materials, such as polyvinyl chloride (PVC) and polyolefins, and even other fluoropolymers do not have the same balance of properties that PVDF provides.
One problem with PVDF, is the relatively high cost. The cost of a PVDF conduit can be lowered by adding fillers, including inorganic fluoride fillers, as described in U.S. patent application Ser. No. 11/158,235. Unfortunately the physical properties of the filled materials are not as good as non-filled PVDF structures, tending to be stiffer and have marginal crack resistance.
U.S. Pat. No. 4,322,260 described the use of acrylonitrile/butadiene/styrene polymer foam as the insulation in double-walled conduit structures. Foamed fluoropolymers mixtures of ethylene/tetrafluoroethylene and ethylene/chlorotrifluoroethylene have been used as an insulation directly on wire or cable, as described in U.S. Pat. No. 5,770,819. U.S. Pat. No. 6,231,919 describes an advantage using a solid or liquid blowing agent rather than gases for producing foamed fluoropolymers wire coatings. The useful fluoropolymers are listed as fluorinated ethylene-propylene, and perfluoroalkoxypolymers (such as tetrafluoroethylene and perfluoropropylvinylether. None of these references describe a foamed fluoropolymer conduit, and none describes polyvinylidene fluoride foam.
A polyvinylidene fluoride foam is described in U.S. Pat. No. 7,081,216. The foam is produced by freezing a PVDF emulsion, followed by thawing.
It has now been found that a polyvinylidene conduit can be formed using foamed PVDF. The foamed conduit is lighter, more flexible, and less expensive than solid PVDF conduit, while retaining good physical properties and flame and smoke resistance.